Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$131.50	3.872%	$136.5917	$136.59	$136.60	$136.60
Purchase #2	$198.79	12.329%	$223.2988	$223.30	$223.30	$223.30
Purchase #3	$45.75	13.330%	$51.8485	$51.85	$51.85	$51.80
Purchase #4	$200.27	11.772%	$223.8458	$223.85	$223.85	$223.80
Purchase #5	$69.33	12.718%	$78.1474	$78.15	$78.15	$78.10
Purchase #6	$139.54	6.724%	$148.9227	$148.92	$148.90	$148.90
Purchase #7	$64.50	13.132%	$72.9701	$72.97	$72.95	$73.00
7 purchase totals =	$849.68		$935.6250	$935.63	$935.60	$935.50